Interior absorptive panel

ABSTRACT

Perforated blankets of fiberglass material are fitted on each side of a double-dimpled core material having perforations therethrough. A backing sheet and face sheet of panel material is bonded to the outer surfaces of the dimples. Sound passing through the face sheet material enters the panel and is dissipated in the fiberglass material in the core. The panel has no resonant frequency and has a high coefficient of absorption over a broad band of frequencies in the speech frequency range.

United States Patent [72] inventor Flyodd A. Martin Fountain Valley,Calif. [21] Appl. No. 863,239 122] Filed Oct. 2,1969 [45] Patented Aug.10, 1971 [73 l Assignec McDonnell Douglas Corporation [54] INTERIORABSORPTIVE PANEL 3 Claims, 3 Drawing Figs.

[52] US. Cl 52/145, 52/618 [51] Int. Cl E04b 1/82, E04c 2/32 [50] Fieldof Search 52/144, 145, 613. 615,618, 624, 625

[56] References Cited UNITED STATES PATENTS 1,961,374 6/1934 Mazer52/144 3,013,641 12/1961 Compton.. 52/615 3,231,454 1/1966 Williams161/68 3,430,405 3/1969 Alder et a1. 52/615 FOREIGN PATENTS 151,4745/1953 Australia 52/618 424,620 5/1933 Great Britain... 52/618 1,024,8891/1953 France 52/618 1,180,504 10/1964 Germany 52/615 Primary Examiner-Frank 1.. Abbott Assistant Examiner---.lames L. Ridgill, .lr.

Attorneys-Walter .1. Jason, Donald L. Royer and Robert 0.

Richardson Patented Aug. 10, 1971 I I I INVENTOR. fiyaw 4. M2770INTERIOR ABSORPTIVE PANEL BACKGROUND OF- THE PRESENT INVENTION Strong,lightweight panels are used in walls, floor or ceiling 5 structures inbuildings and vehicles, such as airplanes, trucks,

trailers, and the like, where the strong lightweight member is desired.One form of panel comprises an inner membrane having protruding nodes oneach side of its planar surface to space and support cover sheets bondedthereto. This provides BRIEF SUMMARY OF PRESENT INVENTION ,Adouble-dimple core is formed in the manner similar to prior art methodsexcept that the sheet of core material has a plurality of smallapertures therein and, when the forming process has been accomplished,these apertures remain unchanged on the nodes but are elongated in thetruncated 1 conical walls interconnecting the opposing nodes. Havingthus modified the prior art double dimpled core, layers of fiberglassbatting with apertures therein are then placed over the nodes and intothe air spaces between the nodes. These spaces-form. cavities whenopposed panel sheets have been glued to the nodes. A face sheet havingapertures therein faces the direction of noise to be attenuated, oninstallation of the panel. An open weave fiberglass flyscreen may beaffixed to- The walls adjacent indentations I2 (and 14) extending in thesame direction meet in a saddle 26 which is in the plane of the originalsheet before it was dimpled. This is also a midpoint between theupwardly extending indentations l2 and the downwardly extendingindentations 14. This distance between saddle 26 and thesurface of thenodes determine the thickness of the fiberglass batting 28 and 30 whichis then applied to each side of the sheet I0. Batting 28 and 30 have aplurality of apertures defined' by aperture walls 32 and 34 adapted tofit over indentations l2 and 14 of cure it) so that the surfaces ofnodes 16 and 18 remain the outermost surfaces of the com bination forattachment with cover and backing sheets. FIGv 2 is an elevational viewshowing the batting 28 and 30 positioned over the core 10 with nodes 16and 18 extending through aperture walls 32, 34 of the batting. As can beseen, the thickness of the batting is substantially the same as thedistance from saddle 26 to the nodes I6 and 18. In order to maintain thebatting and the core in this position, an open weave fiberglassflyscreen 36 and 38 is applied over the batting and in contact with thenodes 16 and 18. This flyscreen may be tacked, glued or bonded in anyappropriate manner to these nodes to thus form an integral inner corestructure.

Because the flyscreen is open face, it does not interfere with thesubsequent bonding of the outer back and face sheets.

In FIG. 3 face sheet 40 and back sheet 42 are shown affixed to nodesI6and I8. Panel 40 is intended to face a noise source the nodes afterthe fiberglass batting has been placed thereover to provide a unitarycore structure for convenient storage and shipping without the outersheets affixed thereto.

i BRIEF DESCRIPTIONOF THE DRAWINGS FIG. I is an exploded perspectiveview of the inner core 'material sandwiched between layers of fiberglassbatting;

FIG. 2 is a sectional view of the inner core composite; and FIG. 3 is asectional view of a completed absorptive panel;

DETAILED DESCRIPTION OF ILLUSTRATIVE' EMBODIMENT Referring now to thedrawings there is shown in FIG. a; core sheet 10 which has been formedfrom a single flatsheet and which has upwardly extending indentations I2and opposite or downwardly extending indentations 14. These in- No.2,441,476 to Ewald for Reinforced Structural Sheet on'lrl.

May I948. These indentations l2 and 14 terminate innodes l6 and '18having a flat surface of a configuration similar to the" forming surfaceof the pins or protrusions of the device used in: forming theindentations.

Before the indentation operation has been made, sheet ltl has aplurality of apertures 20 cut therein. These'openings comprise from fiveto 20 percent of the total area of the sheet before indentation. Theseapertures 20 within the areaof the nodes 16 and 18, retain theiroriginal configuration, whereas the apertures 22 within the truncatedconical wall 24interconnecting the nodes 16, I8 deform with thematerial. and. become elongated. The apertures 20 assist in bonding the;outer' backing and face sheets to the nodes 16- and I8.aswillibedescribed hereinafter, and the elongated apertures-22. have an.acoustical purpose, as will be set .forth hereinafter, also.

and has a plurality of apertures 44 therein. These apertures preventpanel 40 from having a sound amplifying effect similar to that of a drumhead in the absence of openings therein. Sound waves thus may passthrough these apertures 44 and into the fiberglass batting 28 on thenoise side of the dimpled core 10. The apertures 22 in the walls of theindentation permit sound. wave passage therethrough and into the batting30 where further sound absorption occurs.

It is to be understood that the area of the elongated apertures 22,the-areaof the core wall material 24, the core thickness between nodes16 and I8, their offset spacing and the configuration of the nodesthemselves, all contribute to a strength-to-weight relationship and astrength-to-noise-abatement relationship, andthat these parameters maybe varied according to the use of the panel and the characteristicsdesired; In one'form the core material was a thermoplastic materialcalled polysulfone, anopaque creme-colored plastic in its natural form.It has high temperature resistance and low smoke characteristics, makingit a desirable core for interior aircraft panels. In this applicationthe high frequency componentsofnoise wasabsorbedin the light, looselyfilledfront cavity of the core/Whereas normally the' lower'frequency Ye'o'mponentswere allowed to pass through the core perforatioris and'were absorbed by the more dense closely packed fiberglass in the backcavity, in this particular application sufficient'noise. attenuation wasaccomplished without perforatingthecore and using. the back cavityfiberglass.

I claim:

I. A..panel" having a high coefficient of absorption over a broadband offrequencies comprising:

an inner double-dimple core having alternate upwardly and downwardlyextending indentations terminating in nodes ortrbothsides with truncatedconical walls interconnecting opposing nodes, elongated apertures insaid truncated conical walls, 'saidgcote defining aplane between said,nodes, said nodes having, flat surfaceswith apertures therein,said'wallsextendingin the same direction forming a saddle in said plane,first layenof'acoustic material having apertures therein and of'i athickness substantially equal to the space between said saddle and saidnodes, said layer being positioned'zover said! core with-apertures insaid layer being adapted to fit over said indentations and therebyexposing said-l nodes,

aise'eondllayer of'aeoustic material similar to said first layeranti-applied totheother si'dc ofsaid' core, 7

Llt

packed to absorb the lower frequency components of noise in the speechfrequency range.

3. A panel as set forth in claim I, and an open weave material affixedto said nodes to retain said layers thereover.

1. A panel having a high coefficient of absorption over a broad band offrequencies comprising: an inner double-dimple core having alternateupwardly and downwardly extending indentations terminating in nodes onboth sides with truncated conical walls interconnecting opposing nodes,elongated apertures in said truncated conical walls, said core defininga plane between said nodes, said nodes having flat surfaces withapertures therein, said walls extending in the same direction forming asaddle in said plane, a first layer of acoustic material havingapertures therein and of a thickness substantially equal to the spacebetween said saddle and said nodes, said layer being positioned oversaid core with apertures in said layer being adapted to fit over saidindentations and thereby exposing said nodes, a second layer of acousticmaterial similar to said first layer and applied to the other side ofsaid core, said indentations defining unfilled cavities within saidtruncated walls between said nodes and said core plane.
 2. A panel asset forth in claim 1 wherein said first layer loosely fills spacebetween said saddle and said nodes for absorbing high frequencycomponents of noise in the speech frequency range, and said second layeris more dense closely packed to absorb the lower frequency components ofnoise in the speech frequency range.
 3. A panel as set forth in claim 1,and an open weave material affixed to said nodes to retain said layersthereover.